A supercharger is widely used as an auxiliary device for obtaining high combustion energy in an internal combustion engine. For example, an exhaust turbine type supercharger is configured such that a compressor compresses air to be supplied to an internal combustion engine by driving a turbine connected coaxially with the compressor using exhaust gas of the internal combustion engine.
In recent year, there is a growing demand for reducing noise of a supercharger. Patent Document 1 discloses a silencer for reducing noise on an air discharge side of a compressor of a supercharger. This silencer includes a pipe connecting an outlet pipe of the compressor of the supercharger to an air cooler with a double pipe structure formed of an outer pipe and an inner pipe. Between the outer pipe and the inner pipe, a resonance cavity is defined, and the inner pipe is provided with a plurality of through holes communicating with the resonance cavity. It is disclosed that this structure allows the reduction of wind noise with a frequency corresponding to the rotational speed and the number of blades of a compressor impeller by setting the volume of the resonance cavity, as well as the cross-sectional area and the length of the through holes, in accordance with a resonance frequency corresponding to a blower rotational period.